Fast and portable phantom-based calibration for freehand 3D ultrasound

Freehand 3D ultrasound enables volumetric reconstruction by determining the spatial transformation between a tracked probe and the image plane. Portable probes require frequent recalibration due to limited battery life, demanding a fast and practical calibration method. We present an approach using a dual-purpose phantom as both a tracking tool and imaging target. Optical tracking combined with ultrasound imaging of the calibration pins establishes 2D–3D correspondences for least-squares estimation of the image-to-probe transformation. Leave-one-out evaluation showed high accuracy, with errors below the scanner’s resolution. Calibration accuracy is limited by the ultrasound slice thickness.